1. Field
This invention relates to an improved spoked print wheel serial printer or typewriter and more particularly, to one having plural spoked wheels and a single print hammer.
2. Description of the Prior Art
Prior art serial printers have included those incorporating a spoked wheel print element. The wheel is rotated to effect placement of a desired character bearing spoke at a print position. A print hammer is thereafter actuated to drive the selected spoke against a print ribbon and paper located on a platen to effect character printing. The wheel, wheel drive system and hammer are usually mounted upon a carrier which is horizontally advanced along the print line for serially printing characters. Such printers often are associated with character selection keyboards and form a typewriter when so combined. When used as a typewriter, approximately one hundred different print characters are located on the print wheel and may be selected from keyboard operation. Such print wheels are typically 7-9 centimeters in diameter, a dimension governed in part by the number of characters.
Often, it is necessary to type special characters such as, for example, Greek symbols or scientific symbols when preparing documents. When such symbols are desired, the typist must change the print element or print wheel to one which includes such symbols. The print element is thereafter changed when keyboarding normal text. When the printer is used in conjunction with a storage device, the print wheel must be changed during automatic playout operation. It would thus be desirous to include additional special characters or character sets on the same print wheel. However, each character spoke added to the print wheel causes the diameter of the wheel to be increased in order to spacially accommodate the added character spoke. As the wheel diameter is increased, its inertia is increased thereby requiring more expensive and heavier wheel selection drive systems. Further, the carrier drive systems become heavier in order to move the increased weight of the wheel drive selection system. Additionally, more characters result in slower character access times and a resultant speed decrease of the printer, particularly when used in an automatic playout mode. Further, as more characters are added, the character selection logic and drive system become more complex and expensive.
A further desirable typewriter feature is the ability to print exceptionally large characters which are used, for example, when preparing bulletin board notices, speeches to be read, or documents for the visually impaired. Large characters require large space occupancy on the print wheel again resulting in increased diameter wheels with the resultant disadvantages of added weight, added inertia, slower selection speed and increased costs as previously described.